Custom Female-to-Male Thread Adapters & Hex Reducing Bushings

What a Female-to-Male Adapter Does

A female-to-male adapter has an internal (female) thread on one end and an external (male) thread on the other. It screws over a male thread on one side and into a female port on the other — reducing and converting the size in a single part. When the body carries wrench flats, this same part is called a hex reducing bushing; without them, a round reducer. It is the workhorse of pipe, hydraulic and instrument connections.

If instead you need a male thread on both ends, you want a male-to-male adapter; unsure which gender, start with the thread adapter types guide.

Body & Ends We Machine

Choice	Options	When to pick it
Body form	Round, or hex for a spanner	Hex where the joint is torqued (pipe, hydraulic)
Seating	Shoulder stop, or fully threaded (shoulderless)	Shoulder for a set position; shoulderless for max engagement
Female end	Metric, UNC/UNF, BSP (G / Rc), NPT	Screws onto the male part you already have
Male end	Metric, UNC/UNF, BSP, NPT, parallel or tapered	Screws into the port you are adapting to
Sealing	Tapered self-seal, O-ring groove, bonded seat	Matched to the pressure and medium

Standards we cut to: ISO 261 / DIN 13 (metric), ASME B1.1 (UNC/UNF), ISO 228-1 (BSP parallel), ISO 7-1 · ASME B1.20.1 (BSP taper / NPT), BS 84 (Whitworth).

Which Material? Cost, Corrosion & Sealing

Material	Density	Why choose it for a reducing bushing
Brass (CZ121 / C360)	8.5 g/cm³	The default — free-machining, seals well, low cost
Stainless 304	7.9 g/cm³	The most common all-round stainless — general corrosion (303 free-machining on request)
Stainless 316L	8.0 g/cm³	Marine, chemical, washdown, semiconductor
Steel (zinc-plated)	7.85 g/cm³	High-pressure hydraulic strength at low cost
Aluminum 6061	2.70 g/cm³	Light, low-pressure, weight-sensitive
Titanium Gr5	4.43 g/cm³	Light + corrosion-proof — premium and aerospace

The Jobs That Land on Our Bench

Every size pair we machine — M6 to M64

Each row is a pair, with the number that actually decides it. The Also written column gives the naming both ways round, because roughly half of enquiries name the small thread first. Coarse-to-coarse appears at every size step; fine pitches appear on the male end throughout and on both ends within three steps. A pair that is not listed is machined the same way.

The wall in the shank is the number to read first. A female-to-male adapter has a female bore drilled back into a male-threaded shank, and what is left between the male thread root and the female tapping drill is all the metal there is. Above about 2 mm the female thread runs full depth into the shank. Between 1.2 and 2 mm the shank is thin and the collar has to carry the engagement, which means the collar gets longer rather than the bore getting deeper. Below that, the female thread stays in the collar altogether and the shank is left solid.

Where the catalogue stops on this part

On material: 1.4301 for general work, 1.4404 where salt or chemicals are involved, 1.4305 free-machining where the part is nearly all thread. 6061 and 7075 are available for weight-driven work, but a female thread in aluminium galls and strips at a fraction of the torque stainless takes — if the joint gets a torque figure we quote stainless and say why.

What one of these costs

Why every part is priced differently

There is no catalogue number to look up, so the quote is built from the part. These are the eight things that move it, roughly in order of how much they move it:

• Machining time — One male thread turned and one bore drilled and tapped back into the same shank, in one setup where the wall allows it. Where the wall is thin the collar grows instead, and a longer collar is more turning, not less.
• Material — 1.4305 for thread-heavy parts, 1.4404 for salt and chemicals. Brass is cheaper to cut and is the right answer on instrument and low-pressure fittings where the strength is not needed.
• Part dimensions — The male thread sets the bar. The female end is drilled out of that same bar, so a large reduction costs no more stock than a small one - which is the opposite of what the wall table might suggest.
• Tolerance — 6g outside and 6H inside, both standard. A sealing face or O-ring groove on the collar is where a real tolerance starts to cost something.
• Geometry — The tight-wall pairs are the expensive ones. When the wall drops under about 1.2 mm the female thread cannot run into the shank, so the collar has to be longer or the part goes two-piece - both add time the size difference alone does not predict.
• Surface finish — As-machined included; passivation and plating are separate operations with batch minimums.
• Quantity — Setup dominates a one-off. A batch of ten is where the unit price drops sharply, a hundred is where bar is bought to size.
• Inspection — Go/no-go on both threads, plus a check on the wall where the pair is one of the tight ones - that is the dimension that decides whether the part survives being spannered.

Which is why the honest answer to “what does a thread adapter cost” is a question back: two thread designations, the length, the material and how many. With those four we quote within 12 hours, and we quote the part you actually need rather than the nearest thing in a catalogue.

When the hexagon itself is the spec — a male-female hex thread adapter with a called-out SW, a non-standard spanner width, or an inch-metric hex bushing — that side is covered on custom hex thread adapters.

Frequently Asked Questions